Cheryl Bender, program manager for American Red Cross Disaster Services - Southern Arizona, talks with Barb Johnson, far left, and Leanne Mac, inside the Kirk-Bear Canyon Library on July 3, 2017. Both women evacuated from Summerhaven Monday morning due to the Burro Fire. The Red Cross set up an information center for evacuees at the library.

Mamta Popat / Arizona Daily Star

A DC-10 VLAT (Very Large Air Tanker) from Mesa Gateway Airport turns to make a retardant drop on the Burro Fire burning in the Santa Catalina Mountains northeast of Tucson, Ariz. on July 3, 2017.

Smoke kicks up over the Burro Fire as a crew from Eldorado National Forest in California heads up Catalina Highway on July 5, 2017, northeast of Tucson, Ariz.

Mike Christy / Arizona Daily Star

The Burro Fire in the Santa Catalinas continues to grow, with about 21,000 acres burning by Tuesday afternoon. Residents, campers and hikers have been forced to evacuate from the mountain.

Fire crews are working to improve protective barriers around the fire, focusing on strengthening defense lines and finalizing contingency plans for structure protection for possible fire movement in that direction, incident commander Bea Day said in a press release Tuesday morning.

Dry grass and brush, high temperatures and erratic outflow winds have contributed to the fire's spread, Day said.

Officials said at a meeting Monday evening at Sahuaro High School that they cannot give a timeline right now on when residents on Mount Lemmon will be allowed back into their homes.

Day said there needs to be some rainfall on the fire before officials can start looking at when residents can return.

She said the highway up to Mount Lemmon and the Mount Lemmon control road on the back side of the mountains are going to be used as fire breaks for the fire, if needed. Crews need to operate on the roads without public traffic in order to remain safe, she said. Both roads will remain closed to the public for now, officials said.

Those plans can change, Day said, if there is significant rainfall on the fire in the next few days.

George Atkinson, middle, Bea Day, left, and Jay Lusher, of the Southwest Area Incident Management Team, confer about the Burro Fire at Sahuaro High School.

Mamta Popat / Arizona Daily Star

Summerhaven was evacuated Monday morning. Fire crews have been working to determine where to provide structure protection, officials said at the meeting. Crews evaluate structures closest to the fire and work their way to structures farther away.

Officials said homes in the the Willow Creek area are being evaluated for protection, but officials don't believe the fire will reach those homes. The edge of the fire is about 1½ miles from Willow Creek area, officials said.

The Burro Fire burning since Friday around Redington Pass has charred several thousand acres.

On Sunday, evacuations were ordered from the base of Mount Lemmon Highway to the Palisades Visitor Center at milepost 20 as the Burro Fire expanded to about 8,000 acres.

Pima County Sheriff’s deputies assisted in sending campers and hikers within the evacuation zone down the mountain throughout the afternoon. Anyone north of Palisades, including in Summerhaven, were told to evacuate Monday morning.

Leanne Mack, manager of the Mount Lemmon General Store and Gift Shop, said she and her parents evacuated their homes around 9:30 a.m. Monday.

Cheryl Bender, program manager for American Red Cross Disaster Services - Southern Arizona, talks with Barb Johnson, far left, and Leanne Mac, inside the Kirk-Bear Canyon Library on July 3, 2017. Both women evacuated from Summerhaven Monday morning due to the Burro Fire. The Red Cross set up an information center for evacuees at the library.

Mamta Popat / Arizona Daily Star

She said she doesn’t know yet when the roughly 40 other full-time Summerhaven residents will be allowed back into their homes.

“It’s smart that they did what they did,” Mack said of the evacuation. She said she was worried the fire would jump the Mount Lemmon Highway and leave them stranded. Her vehicle couldn’t handle the only other road, which is more primitive than the highway, down from Mount Lemmon.

“We’ve done this before. We did it for the Bullock Fire,” Mack said.

“We understand this decision is sudden, however based on the activity of the fire, this is the safest and best decision for our residents,” a post on the Coronado National Forest Facebook page said Sunday afternoon.

Summerhaven residents were told at an update Sunday evening that they were allowed to come and go up the mountain as long as they showed proof of residency, but were asked to get their belongings ready in case they were asked to leave. The Sheriff’s Department issued the evacuation notice for Summerhaven after 10 p.m.

Lieutenant Jeff Copfer, Rincon District commander for the Pima County Sheriff's Department, estimated at the evening update that Mount Lemmon Highway would be closed to visitors for at least "several days."

The Burro Fire was first reported on Friday morning in the foothills of Redington Pass near Burro Tank and was fueled primarily by tall grass and brush on steep, remote terrain, according to the U.S. Forest Service.

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A DC-10 VLAT (Very Large Air Tanker) from Mesa Gateway Airport turns to make a retardant drop on the Burro Fire burning in the Santa Catalina Mountains northeast of Tucson, Ariz. on July 3, 2017.

Rick Wiley / Arizona Daily Star

Southwest winds on Saturday pushed the fire to the east, an update from the forest service said, with smoke plumes visible from Tucson. Aerial resources, including three helicopters and three air tankers were utilized to reduce the fire’s spread.

By Sunday afternoon, a Type 1 Incident Management Team had been assigned to the fire. Day said at the evening update that the Burro fire was in the "fire scar" of the Bullock Fire, which destroyed more than 30,000 acres in 2002.

Day said early efforts to use retardant to slow the Burro Fire were unsuccessful.

"We couldn't get the firefighters on the ground," Day said. "For it to be effective, you have to have boots on the ground. In the area it is in, it is too dangerous to put firefighters."

Fire managers are using air power to attack the Burro Fire at about MP 7 north of Redington Road in Coronado National Forest.

Mike Christy / Arizona Daily Star

There are 594 total personnel assigned to the fire as of Tuesday night.

Because of rugged and inaccessible terrain, firefighters have been using indirect tactics to fight the fire, while crews have been implementing structure protection along Catalina Highway, according to the U.S. Forest Service.

The cause of the fire is still under investigation.

The Burro Fire is one of five active fires in the Coronado National Forest, including the Frye Fire which has burned more than 45,000 acres around Mount Graham.